Plate-shaped sound-absorbing element



March 12, 1963 E. GROHMANN PLATE-SHAPED SOUND-ABSORBING ELEMENT Filed April 11, 1961 FIG.

INVENTU/P Emil Grohmann ATTY-S'.

United States Patent ()fiice 3,080,938 Patented Mar. 12, 1963 v 3 080,938. PLATE-SHAPED SOUhlD-ABSORBING ELEMENT Emil Grohmann, 69C Waltgeristrasse, Herford, Westphalia, Germany Filed' Apr. 11, 1961', Ser. No. 102,219 3 Claims. (Cl. 18133) This invention relates to a plate-shaped sound-absorbing element which consists of a highly porous foamed material such as a synthetic foamed material and is intended to serve for the absorption of sounds in rooms, and is a continuation-in-part of the application filed by me on April 23, 1956, Serial No. 579,894, now abandoned, I

and embodies improvements in the art thereover.

It is the object of the present invention to considerably improve the known plate-shaped elements for the absorption of sounds in rooms,'this being achieved in a simple manner in that fine channels are pierced with the aid of needles or the like in an element of the aforementioned kind to be fitted to walls or the like. Thereby deeply penetrating and branching sound-absorbing passages are produced because a large number of consecutive and juxtaposed. closed pores of the material used are pierced. The plate-shaped element is pierced to such an extent from one side thereof that a diaphragm-like unpierced portion remains on the opposite side of the element, which portion has a thickness including one to three closed pores. Preferably, highly porous plates consisting of foamed polystyrene with closed pores are used which have an approximate thickness of mms. and are pierced by 350,000 to 450,000 needles per sq. meter plate surface area. The plates are preferably pierced by the needles to the extent mentioned perpendicularly to their plane. In a preferred embodiment, although not shown in the specification, the needles have a diameter of 0.6 to 1.4 mms.

A preferred embodiment of the invention will now be described by Way of example and with reference to the accompanying drawing, in which:

FIG. 1 is a top plan view of a plate-shaped soundabsorbing element according to the invention consisting of sponge or crepe polystyrene;

FIG. 2 is a vertical cross section through the element of FIG. 1, showing the diaphragm-like portion remaining unpierced, and

FIG. 3 is a fragmentary view similar to FIG. 2, on a larger scale.

In order to obtain an effective sound absorption in a room, the walls and/or the ceiling of the room are provided with a special type of plates. The carrier for these plates may be the surface of a Wall or ceiling, wall-paper, a paper layer or any other support such as plates of the same or other material or a layer of plaster or the like.

FIG. 1 shows a plate-shaped sound-absorbing element 10 which consists of foamed polystyrene. This element is 10 mms. in thickness and 98% of its volume consists of irregularly shaped and randomly located, closed pores 11 which range from 0.1 to 0.4 mms as a maximum dimension. As shown in FIGS. 2 and 3, a multiplicity of very fine channels 12 having a diameter of 0.6 to 1.4 mms. are pierced in the element 10 perpendicularly to the plane thereof by means of needles which have a diameter of 0.6 to 1.4 mms. The channels 12 are pierced in the element 10 from one side thereof to such an extent that a thin diaphragm-like portion remains unpierced on the opposite side of the element. This portion of the element 10 has a thickness including only one to three closed pores '11, that is to say, that two to four walls 13 of pores are contained in this portion which are not pierced by the needle-s, whereas in the remaining portion of the element 10 a large number of consecutive and juxtaposed pores 11 are intersected by the channels 12.

The channels formed by the needles will terminate from 0.1- to 1.2 mms. from the imperforate surface of the element 10 sincethe cells range from 0.1 to 0.4 mms.

Such an element of foamed polystyrene which is nearly entirely pierced and the closed pores of which are intersected by the pierced channels, has the essential advantage that the sound can penetrate into the element without hindrance also from the side formed by the diaphragmlike portion. The dynamic flow resistance of the element having this portion is equal to that of a plate-shaped element which is entirely pierced since the total thickness of the Walls of pores remaining unpierced is extremely small. The passage of the sound through the side of the'element formed by the diaphragm-like portion is not dependent upon the total thickness of this portion but upon the thickness of the unpierced walls of the pores.

The diaphragm-like portion of the element prevents any disadvantageous circulation of air through the element. The heat-insulating effect of the element according to the invention is equal to that of a plate-shaped element of the same material having no channels pierced'therein.

It is particularly important and advantageous that the elements of the invention, besides producing an excellent sound-absorbent and heat-insulating effect, also possess the property that the holes are not visible from a short distance, so that the architectural appearance, for example of a ceiling, is not impaired in any way.

When using a synthetic foamed material composed of polystyrene, for example that known under the trade name of Styropor, 98% of thevolume of which consists of closed pores of a diameter of about 0.2 mms., and which is in the form of a plate having a thickness of 10 mms. and pierced by 400,000 needles per sq. meter surface area, the needles having a diameter of 0.8 to 1.2 mms. and a length of 80 mms., the following sound-absorbing values are obtained:

500 Hertz-30 to 35% sound absorption (measurements in the acoustically live room according to Sabine; the sound-absorbing plate-shaped elements stood at a distance of 4 cms. from the sound-reflecting surface),

1,000 Hertz70 to sound absorption,

1,250 Hertz-% sound absorption,

5,000 Hertz62% sound absorption.

As compared with the known sound-absorbing plates the absorbent values of the plate-shaped elements according to the invention are higher by 200 to 350%.

The plate-shaped sound-absorbing element can be subsequently mounted on the surface of existing firm carriers or be fitted together in mosaic fashion with supporting strips or frames or the like made in a factory. The elements are water and moisture repellent. They may be colored or provided with a coating of fire-proof paint. They can be secured to plaster or wood surfaces by gluing, sintering or nailing.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

I claim:

1. An acoustic tile comprising a block of foamed polystyrene having a plurality of closed, irregularly shaped and randomly located cells ranging from 0.1 to 0.4 mms., said block including opposed surfaces and a plurality of needle-like channels ranging from 0.6 to 1.4 mms. in diameter and extending from one of said surfaces to a point spaced from 0.1 to 1.2 mms. from said other opposed surface, said other opposed surface being substantially imperforate and each of said needle-like channels being closed by at least one closed cell.

2. An acoustic tile as set forth in claim 1 wherein said needle-like channels are disposed from 350,000 to 450,000 channels per square meter of block surface.

3. The structure of claim 1 wherein said cells comprise substantially 98% of the volume of said block and said block is 10 mms. thick and said channels are 8.0 mms. deep.

References Cited in the file of this patent UNITED STATES PATENTS Rosenblatt Mar. 18, 1930 Mazer May 12, 1931 New Feb. 13, 1934 Gessler et al July 31, 1951 Page Nov. 16, 1954 Sabine June 27, 1961 

1. AN ACOUSTIC TILE COMPRISING A BLOCK OF FORAMED POLYSTYRENE HAVING A PLURALITY OF CLOSED, IRREGULARY SHAPED AND RANDOMLY LOCATED CELLS RANGING FROM 0.1 TO 0.4 MMS, SAID BLOCK INCLUDING OPPOSED SURFACES AND A PLURALITY OF NEEDLE-LIKE CHANNELS RANGING FROM 0.6 TO 1.4 MMS. IN DIAMETER AND EXTENDING FROM ONE OF SAID SURFACES TO A POINT SPACED FROM 0.1 TO 1.2 MMS. FROM SAID OTHER OPPOSED SURFACE, SAID OTHER OPPOSED SURFACE BEING SUBSTANTIALLY IMPERFORATE AND EACH OF SAID NEEDLE-LIKE CHANNELS BEING CLOSED BT AT LEAST ONE CLOSED CELL. 